1. Biophysics Program, Stanford University, Stanford, CA 94305, USA.
2. Department of Bioengineering, Stanford University, Stanford, CA 94305, USA.
3. Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA.
4. Department of Applied Physics, Stanford University, Stanford, CA 94305, USA.
5. Department of Biology, Stanford University, Stanford, CA 94305, USA.